And just set for Project, and all single source layouts will use it? (Sorry for so many questions, I can't test until I get dev to deploy again, so I want to make sure I understand completely before checking in)

Yes, that's the spot - you can also change the mouse-over text too. I've got "Contents/Search/Index" subbing for "Show" and mouse-over text of "Show Table of Contents, Search & Index buttons" for one of my projects because in my SSL recipe I changed the default order of the buttons to promote Search over the index. To use it with other projects, you need to make a copy of the .lng file and save it outside of the project. Then when you create a new project, just copy it back in overtop of the existing .lng file. Just keep a list of what customizations you made because I found that when changing versions of RH, they (Adobe) sometimes change the internal structure and you will cause an error in your project when you sub in an older version copy of the .lng file (voice of experience here </laugh>). Then you will need to do those customizations again & save another copy out.